Search results for "Subduction"
showing 10 items of 166 documents
The architecture and Neogene to Recent evolution of the W Calabrian continental margin: an upper plate perspective to the Ionian subduction system (C…
2010
The western Calabria continental margin forms the transition between the Pliocene to Recent Marsili spreading center and continental Calabria, all parts of the upper plate of the Ionian subduction zone. Integrating high-resolution and crustal seismic images constrained by gravity modeling, we provide a detailed reconstruction of the architecture of the margin and develop a new scheme for its Miocene to present evolution. This time span encompasses the continent-continent collision between Africa and Eurasia, subsequent orogenic collapse and rifting apart between the two continental masses, and the Pliocene to Recent emplacement of oceanic crust in the Vavilov and Marsili basins. The crust o…
Evolution of Cambrian and Early Ordovician arcs in the Kyrgyz North Tianshan: Insights from U-Pb zircon ages and geochemical data
2019
Abstract Geochronological, geochemical, and structural studies of magmatic and metamorphic complexes within the Kyrgyz North Tianshan (NTS) revealed an extensive area of early Palaeozoic magmatism with an age range of 540–475 Ma. During the first episode at 540–510 Ma, magmatism likely occurred in an intraplate setting within the NTS microcontinent and in an oceanic arc setting within the Kyrgyz-Terskey zone in the south. During the second episode at 500–475 Ma, the entire NTS represented an arc system. These two phases of magmatism were separated by an episode of accretionary tectonics of uncertain nature, which led to obduction of ophiolites from the Kyrgyz-Terskey zone onto the microcont…
The demir kapija ophiolite, Macedonia (FYROM): A Snapshot of subduction initiation within a back-arc
2013
The Demir Kapija ophiolitic complex in southern Macedonia–FYROM (Former Yugoslav Republic of Macedonia) represents the southernmost exposure of the Tethyan Eastern Vardar ophiolitic unit in the Eastern Mediterranean. It consists of a mafic volcanic sequence (pillow basalts, sheeted dyke diabases and gabbros) that was subsequently intruded by island arc magmas with and without adakitic affinity. The mafic volcanic sequence is characterized by slightly increased ratios of large ion lithophile elements to high field strength elements (LILE/HFSE), flat rare earth element (REE) patterns, radiogenic 143Nd/144Nd (up to 0·51272) and high TiO2 contents (which reflect Pl + Ol + Cpx fractionation). Th…
The composition of fluids stored in the central Mexican lithospheric mantle: Inferences from noble gases and CO2 in mantle xenoliths
2021
We present the first isotopic (noble gases and CO2) characterization of fluid inclusions coupled to Raman microspectroscopy analyses in mantle xenoliths from Central Mexico, a geodynamically complex area where the Basin and Range extension was superimposed on the Farallon subduction (terminated at 28 Ma). To characterize the isotopic signature of the Central Mexican lithospheric mantle, we focus on fluid inclusions entrapped in mantle xenoliths found in deposits of the Joya Honda maar (JH), a Quaternary monogenetic volcano belonging to the Ventura Espiritu Santo Volcanic Field (VESVF) in the state of San Luis Potosí (central Mexico). Thirteen ultramafic plagioclase-free xenoliths were selec…
Zircon age and occurrence of the Adaatsag ophiolite and Muron shear zone, central Mongolia: constraints on the evolution of the Mongol–Okhotsk ocean,…
2005
The Adaatsag ophiolite in eastern Mongolia is situated in the Mongol–Okhotsk suture zone, which extends from central Mongolia through Transbaikalia to the Sea of Okhotsk and separates the Siberian and Amurian (Mongolian) plates. The ophiolite sequence passes upwards from serpentinite melange and serpentinized dunite and harzburgite, through layered gabbro (with leucogabbro pegmatite dykes), wehrlite and clinopyroxenite, to isotropic gabbro and leucogabbro, sheeted mafic dykes, and olivine-rich basaltic lavas, overlain by red chert and meta-clastic sediments. A single-zircon mean 207 Pb/ 206 Pb evaporation age of 325.4 ± 1.1 Ma for a leucogabbro pegmatite dyke records the time of igneous cry…
Constraining lithospheric flow.
2016
The motion of Earth's tectonic plates—the lithosphere—is driven by the subduction of relatively cold and dense oceanic plates into the mantle. The resulting forces drive the motions of continental plates, but the manner in which this happens depends on the effective viscosities of the lithosphere and mantle. On page 1515 of this issue, Liu and Hasterok ( 1 ) discuss a novel method of constraining viscosities of the lithosphere from geophysical data.
Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring.
2016
Abstract Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2‐rich gas (CO2/Stotal > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are acc…
On backflow associated with oceanic and continental subduction
2021
SUMMARY A popular idea is that accretion of sediment at a subduction zone commonly leads to the formation of a subduction channel, which is envisioned as a narrow zone located above a subducting plate and filled with vigorously circulating accreted sediment and exotic blocks. The circulation can be viewed as a forced convection, with downward flow in the lower part of the channel due to entrainment by the subducting plate, and a ‘backflow’ in the upper part of the channel. The backflow is often cited as an explanation for the exhumation of high-pressure/low-temperature metamorphic rocks from depths of 30 to 50 km. Previous analyses of this problem have mainly focused on the restricted case …
Pliocene tourmaline rhyolite dykes from Ikaria Island in the Aegean back-arc region: geodynamic implications
2009
Very rare rhyolite dykes cross-cutting a Miocene I-type biotite-granite were discovered on Ikaria Island in the Aegean back-arc region. Their intrusion postdates exhumation of the granite to brittle crust at about 6.0-3.6 Ma; hence a Pliocene age is inferred. Petrological, geochemical and isotopic arguments indicate an origin through melting of crustal lithologies (tourmaline greywackes/semipelites) with no detectable contribution from asthenospheric sources. Strontium isotope ratios are relatively low unlike values for sediments entering the Hellenic trench but similar to those for certain Miocene Cycladic I-type granites and low-Rb Permo-Carboniferous Cycladic basement acid orthogneisses.…
Constraints on mantle source and interactions from He-Sr isotope variation in Italian Plio-Quaternary volcanism
2008
[1] Helium isotope ratios of olivine and pyroxene phenocrysts from Plio-Quaternary volcanic rocks from southern Italy (seven Aeolian Islands, Mt. Vulture, Etna, Ustica, and Pantelleria) range from 2.3 to 7.1 Ra. Importantly, the phenocryst 3He/4He correlate well with whole rock Sr isotopic composition (0.70309–0.70711), reflecting the mixing of two sources. A significant contribution of He from crustal contamination is recorded only occasionally (e.g., pyroxenes from Vulcano). When merged with data from the Roman Comagmatic Province, a remarkably strong near-linear He-Sr isotope correlation is apparent. The general northward decrease in 3He/4He corresponds to an increase in 87Sr/86Sr (and a…